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Old 07-15-2016, 11:18 AM   #1
Tiltin Hilton
Join Date: Jun 2016
Location: Discovery Bay
Posts: 15
Rooftop Solar or Portable-Solar PV 101

Taking a look at Solar (Photovoltaic) for RV use. Solar charging is a great way to provide electricity for RV"s, Boats, Cabins, just about anything. Well we all know that. So what makes a "good" Solar installation? A little about me; I started building Solar Modules (panels) back in 1975. We built mono and poly panels. Trying to aim at the sun with the proper tilt angle was the only way the panels would produce rated power. In 1979, we teamed up with Motorola to design a panel that could lay flat without tilt and produce rated power. To achieve this, we designed a laser beam that would slice the silicon ingots very thin and leave small pyramids on the surface. These would refract sunlight on the solar cells. Worked great, as we used them for a Government B-1 Bomber project. For RV and Marine use, we sold them by the hundreds. We were also one of the largest Arco dealers in the USA. In 1982, I designed and installed the first Solar (PV) system on a home that sold power back to PG&E, located in Palo Alto, California. As more manufactures started in this industry, the panels became more generic, and cheaper.

For RV use, it was the norm to install on the roof. We even made our own rooftop mounting with streamline mounting. We did see power drop off though as the panels would heat up. I wanted to point out the pros and cons on panel mounting. The BIG problem today is the mounting flat with cheaper panels (China) and the burning out of the cells from the heat. In our heavy duty rated panels we used a ribbon connection on the cell, and as the cell would expand in the heat, the ribbon would allow 100% connection. Cheaper panels did not use this and would fail after a couple of hot cycles.

OK-pros and cons for mounting:

-install and forget
-charging when parked or moving

Rooftop cons
-overheat panels loose up to 45% power
-low output due to dirty panels
-non tilt, lower output than rated
-must park in sun, (if it is hot in the sun then RV will need to run AC? with generator?) counter productive.
-additional wind resistance while driving
-damage from trees and overhead

Portable pros
-able to aim directly into sun with proper tilt angle
-park RV in shade while panels are in the sun
-easy to clean and keep at 100% output
-smaller array (panels) for same output-panel cooling from exposed back
-no additional penetrations into roof (leaks)
-easy to store and set up, set panels and plug in
-use less panels for rated output, cheaper
-can be hooked to tow vehicle charging very easy

Portable cons
-set up and take down, actually, quicker than your BBQ
-subject to theft

Hope this helps deciding on Solar.

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Old 07-21-2016, 12:35 AM   #2
Learning a lot as I go...
Join Date: Aug 2015
Posts: 213
Puzzling over this exact topic myself...

Additional downsides to portable:
- storage while not in use.
- monitoring and adjusting throughout day to maintain that best angle

I keep trying to figure out a pole type mount that would be simple enough to store in/on RV and setup (or take down) for shorter stays. Currently leaning towards a 2 section tower type setup but afraid that asthetic may be less than desireable.

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Old 07-21-2016, 11:23 PM   #3
Senior Member
Join Date: Oct 2015
Posts: 872
Room mounting is a no brainer for us. Its convenient and I don't need to worry about theft.

Losses due to not tilting panels easily offset with additional panels-oversizing the system.

Takes me less than 5 minutes to clean my panels with papertowels and windex so that isn't a big issue for us. Great opportunity to inspect the roof for damage and leaks.
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Old 07-22-2016, 12:40 AM   #4
Junior Member
Join Date: Jul 2016
Location: Sparks, NV
Posts: 7
Rooftop Solar

On my 1993 Thor Columbus Class A, I have one 85 watt solar module mounted on a pivoting and tilting rack I built in the past with aluminum angle. My 75 watt thin film module used a simple 4 bracket mount using thumbscrews and various aluminum straps to get a module angle that matches the sun angle at sun noon that varies through the year. These modules feed into #6 appliance cord to a Morningstar 25 amp charge controller that has a digital voltmeter/ammeter and has settings for flooded lead acid or gel batteries (two 6 volt deep cycle and a trip charger that at 14.3 VDC trickle charges the engine start battery . I have had good performance and no overheating as the air space between the coach roof and modules allows air flow in storage and driving, and more air when parked and raised. Fall and spring camping out landsailing in No. Nevada requires parking pointed west on our dry lakes and attending rocket launches, etc. I can supply photos of what I built. Tilt racking is fairly inexpensive and easy to mount. I am planning on using a cord between new tilting panels and solar input port on my 2016 Leprechaun 240FS class C. It's wall construction I am guessing would make an internal wire path to the batteries under the entry step difficult. Any advice would be appreciated. Mark, and electrical engineer with too many hand tools.
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Old 07-22-2016, 12:44 AM   #5
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Join Date: Mar 2014
Location: Mountain Foothills of Southern Alberta
Posts: 666
What temperature are we talking about that the panel will lose 45% of its rated power? Considering that a panel temp of 45 celsius will cause an approximate 10-15% lose.

2007 Surveyor SV230
- 200 Watts Solar/MPPT Controller - 230 AH Battery Bank - 600 watt PSW Inverter - (2) 2000 watt Inverter Generators - LED Lighting - Boon Docking 99% of the time.
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Old 07-22-2016, 01:17 AM   #6
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Location: Sparks, NV
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Solar Module Power Loss at high temps

In my experience with rooftop solar and RV mounted solar systems, when the ambient air temp is near 100F, the dark surface of modules can get to 150F and on windless days, their power output falls off a lot when the module temperature gets up in the 110F and up conditions. In the past I lost a BP Solar module over several years as the the cells in the module tracked with "x"s across some of the cells (mono crystalline silicon). My think film Unisolar module and Chinese 85 watt polycrystalline seem to not have any degradation from storage in the sun in the Reno, NV climate. I can see maximum output of about 8 amps on cold sunny days when the sun angle is 90 deg from the module vertical angle. I use small ropes attached to the lower corner of the 85 watt module to track the sun. it does well adding to the output of my fixed angle thin film module that is physically larger because of it's lower watts/sq ft technology. Mark
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Old 07-22-2016, 07:52 AM   #7
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Join Date: Mar 2016
Location: Alberta
Posts: 77
There is also the portable vs portable "kits" cons to consider

The portable folding style kits you purchase with integrated controller are basically backwards engineered as the controller is installed closest to the panel with a longer run of wire to the battery/trailer connection. The controller should be as closest to the battery as possible.

I am all for a portable system but it does not work for us as we do not spend our day sitting at our trailer. Roof mounted with no roof penetrations for us. Install and forget.
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Old 07-22-2016, 08:44 AM   #8
Junior Member
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Location: Sparks, NV
Posts: 7
Rooftop dolar

Roof mount with cable on the outside to batteries? No penetration of the roof, but as with a ground mount, large enough wire suze( #6 flexible appliance cable or larger keeps the dc volt drop well under 2 volts and a 10 ft wire distance . The controller can be at the module or closer to the batteries. That would be a good experiment. On my class a it is wall mounted inside about halfway between modules and batteries. Since the controllers vary voltage mostly and voltage limiting when the batteries are fully charged, it is not critical where there are located. I like the Morningstar feature of an equalizing charge once a month where the voltage is slightly higher (14.4 v ) for a period of time. My system does require water fills every 3 months with Trojan 6v deep cycle batteries in series.
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Old 07-22-2016, 01:26 PM   #9
Learning a lot as I go...
Join Date: Aug 2015
Posts: 213
Controller location comes down to where you want or can afford voltage drop.

The specs on the panel I have have the panel output somewhat above 12-13v needed by the battery. This is a prime function of the solar controller is to convert the panel output to something better for the battery. So if the panel puts out 16v and the controller puts out 13v and the battery needs 13v I can afford to lose a bit between the panel and controller more than I can afford to lose anything between controller and battery.

Now if the controller had remote voltage sensing... like many car alternator controllers... it could compensate for the drop and it would be a very different situation.
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Old 07-22-2016, 01:51 PM   #10
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Location: Sparks, NV
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I think my Morningstar had that remote feature as it had an extra wire going directly to the + battery post to a sending port. I like the digital meter that shows voltage, solar output in amps, and load amps on a circuit I use for a small non-recording SATV receiver and a Sharp LCD 12 in TV. With a 75 watt inverter, that system uses 36 watts DC.

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